It's because people install malware a lot. Usually it comes along for the ride with pirated software, creating a 2x headache. I remember when they introduced similar policies at Google for Windows workstations - the stated rationale was that Windows users would warez literally anything and this was independent of job role or position. Senior engineering managers would be warezing things and it would come bound to malware. So they moved to binary whitelisting, eventually :(

Linux avoids this problem mostly because it doesn't have much commercial software to pirate in the first place.